1. Field of the Invention
The present invention relates to an encapsulation cap, particularly substrates capable of being attached to its two surfaces and absorbing moisture for structural elements formed on the substrates, and a display device using the same.
2. Description of the Related Art
Organic electroluminescence is the phenomenon that excitons are formed in an (low molecular or high molecular) organic material thin film by re-combining holes injected through an anode with electrons injected through a cathode, and light of specific wavelength is generated by energy from thus formed excitons.
Organic electroluminescent device using the above phenomenon has a basic structure as shown in FIG. 1. Basically, the structure of organic electroluminescent device includes a glass substrate 1, indium-tin-oxide layers 2 (hereinafter, referred as “ITO layer”) formed on the glass substrate 1 and acting as anode electrode, insulating layer, organic electroluminescence layer 3 formed with organic material, and metal layer 4 acting as cathode electrode. Reference mark “W” which is not mentioned above indicates a wall formed to divide the organic electroluminescence layer 3 and the metal layer 4 into a number of sections.
On the other hand, structural elements constituting the organic electroluminescence are well known in the organic electroluminescent device field. Therefore, a detailed description thereon is omitted.
The organic electroluminescence layer 3 which is one of the elements constituting the organic electroluminescent device having the above structure is characterized to be vulnerable to moisture and heat. Accordingly, in order to separate the organic electroluminescence layer 3 from the exterior (atmosphere), a metal cap 10 is fixed to the outer portion of the substrate 1, and so the inner space, that is, each structural element of the device, is sealed. The structure of the metal cap 10 having the above function and bonding process is briefly described below.
In general, the metal cap 10 is divided into a bonding section 11 to be bonded on the outer portion of the substrate 1, a first space section 12 formed at the inner side of the bonding section 11 for receiving the metal layers 4, the organic electroluminescence layer 3 and the walls, and a second space section 13 formed at the inner side of the first space section 12. A getter 6 absorbing moisture is attached to the bottom surface of the second space section 13 by tape 5.
After the above structural elements are formed on the glass substrate 1, a sealant is dispensed on the bottom surface of the bonding section 11 of the metal cap, and the metal cap 10 is then pressurized to the substrate 1 to bond the metal cap 10 on the substrate 1. Accordingly, the structural elements formed on the substrate 1 are completely separated from the exterior by the metal cap 10.
As shown in FIG. 2, on the other hand, in the cellular phone H which has been widely used as communication device, a sub window SW formed on the front surface of the display section D and a main window MW formed on the rear surface of the display section are provided separately. In the current cellular phone, the liquid crystal display (LCD) device is used as the main window MW, and the organic electroluminescence device (OLED) is used as the sub window SW. The main window MW and the sub window SW are designed to be operated and controlled independently by its own electric circuit (memory chip).
Now, the cellular phone has become smaller, and the definition of displayed image has been greatly improved. Thus, technical development has aimed to operate and control the sub window and the main window by constituting them with the organic electroluminescence devices and using one electric circuit (chip).
When the sub window and the main window are constituted with the organic electroluminescence device, special attention should be paid to the structure of the cap, which is one of the elements constituting the organic electroluminescence device as described above, and is used for separating the organic electroluminescence layer from the exterior (atmosphere).
In the case that the sub window and the main window are constituted with the organic electroluminescence device, each organic electroluminescence device used as the sub window and the main window should comprises the cap for protecting the structural elements including the organic electroluminescence layer. However, the cap (shown in FIG. 1) bonded to the substrate increases the size (thickness) of the organic electroluminescence device. In particular, since each organic electroluminescence device includes two caps, the size (thickness) of the finished product, i.e. the cellular phone, cannot but be increased.